The World Health Organization ranks migraine as the 3rd most prevalent disease worldwide and 8th most disabling (4th most in women) making it the most common neurological disorder. One of the primary reasons for the disabling nature of migraine is the poor efficacy of currently available therapeutics. Less than 50% of patients achieve complete relief with acute agents such as triptans and only half of patients achieve 50% relief with preventative agents. Development of new therapeutics has been slow due to a lack of understanding of the underlying pathophysiology of migraine. Our long-term goal is to identify new therapeutic targets for this common and debilitating disorder. One of the most consistent triggers for migraine is administration of a nitric oxide (NO) donor. Approximately 75% of human migraine patients will develop an attack within 6 hours of NO donor administration. Mechanisms by which NO donors trigger migraine are unknown. The objective of this proposal is to test whether the reaction product of NO and superoxide, peroxynitrite (PN), contributes to migraine pathophysiology. Studies over the last decade have shown that PN is an important activator/sensitizer of sensory neurons in preclinical pain models of neuropathic, inflammatory, and cancer pain and agents that eliminate PN have demonstrated efficacy in preclinical pain models. However, no studies have examined whether PN contributes to migraine despite the observation that the only pain state triggered by administration of a PN-producing stimulus is migraine (NO donors do not directly cause other types of pain). Thus, we propose to test the hypothesis that the effects of NO on migraine are due to PN formation. The rationale for the proposed study is that it 1) greatly expands our knowledge of mechanisms underlying one of the most common migraine triggers; and 2) provides translational potential by offering new therapeutic targets for migraine. We will test this hypothesis with 2 Aims using preclinical rodent models: Aim 1 will test the efficacy of PN scavengers and decomposition catalysts against NO donor-induced migraine behavior and NO donor-induced activity in trigeminal (dural) neurons. Aim 2 will test the efficacy of PN scavengers and decomposition catalysts against NO donor-induced mast cell degranulation, CGRP release, and protein tyrosine nitration in the dura. This innovative study will for the first time investigate the role of PN in migraine and will use novel behavioral models that mimic conditions relevant to migraine. The significance of the proposal is that it advances our understanding of migraine mechanisms and has the potential to lead to better therapeutics.